molar ratio, buffer

Question

9. What is the molar ratio [A- / HA] of Na acetate (base) to acetic acid (acid) for a buffer with a pH of 6.4 and a pKa of 6.9?

Answer 1

Henderson Hasselbalch equation:

pH = pKa + log [conj,base] / [acid]

pH = 6.4

pKa = 6.9

[conj,base] / [acid] = ?

Solving for [conj,base] / [acid], we have ....

6.4 = 6.9 + log [conj,base] / [acid]

-0.5 = log [conj,base] / [acid]

[conj,base] / [acid] = 0.316